Method of casting propellant within a rocket motor casing



Dec. 7, 1965 K JR 3,222,433

METHOD OF CASTING PROPELLANT WITHIN A ROCKET MOTOR CASING Filed July 18, 1961 SOLVENT BATH CHANGING FURNACE POLYMERIZING PHASE INVENTOR NICOLAS MAKAY JR BY 7 5 t ATTORNE s United States Patent 3,222,433 METHOD OF CASTING PROPELLANT WITHIN A RUCKET MOTOR CASING Nicolas Makay, Jru, Rua Joaquim Nabuco 179, Apto. 602, Rio de Janeiro, Brazil Filed July 18, 1961, Ser. No. 124,908 3 Claims. (Cl. 2643) The present invention relates to the method of, making rocket motors for missiles, and particularly to a method for making solid propellant filled rocket motors for missiles.

Among prior methods, the propellant is batch mixed in sigma-blade mixers and then the mixture is cast directly into the rocket motor or into molds. In the latter case, the solidified cast mixture is removed from the mold and mounted in a rocket motor. Another prior known method comprises the continuous mixing of oxidizers, fuel and other additives, the mixture then being extruded or poured into molds or into the rocket motor. Because the most efficient mixtures are substantially impossible to cast and are unworkable, less than maximum efficient mixtures are often employed. Thus, for example, ammonium perchlorate oxidizers require, for the highest effect, a mixture of about 90% by weight or 80% by volume. This mixture is not castable so that a less efficient mixture containing less solids is often used.

The mixture of oxidizers and fuel is dangerous to handle, requiring expensive, remotely controlled equipment. Furthermore, the solid-liquid mixture of high solid content is a viscous material which is inclined to retain air bubbles. Since all air must be removed, complicated vacuum casting or forming processes are required.

The principal object of this invention is to provide a method for casting high ei'liciency solid propellant grains directly into the rocket motor.

Another object of the invention is to provide such a method which will eliminate the disadvantages of prior known methods and apparatus.

Still another object of the invention is to provide such a method employing simple and inexpensive apparatus.

Still another object of the invention is to provide such a method that will be safe.

In one aspect of the invention, a rocket motor may comprise a tubular element. A first closure or mandrel may be threadedly mounted into one end of the tubular element of the motor and it may extend through the motor along its longitudinal centerline, forming an annular space therein. After the annular space has been filled with the proper sized oxidizer, which may be one of the many materials that generate oxygen as they are consumed in burning, a closure may be threadedly mounted into the opposite end of the motor. As will be described, the closure members preferably are made of a low melting material so that it can be removed easily. The closures may be held in place by other suitable \nieans. By way of example, the most common oxidizers are potassium chlorate, KClO ammonium perchlorate, NH C lO and ammonium nitrate, NH NO although sodium and potassium nitrates have been used in the past.

In anothei mpect of the invention, both the lower end of the mandrehand the closure may be provided with passageways extending therethrough that communicate with the annular spacewithin the motor that surrounds the mandrel. The tubular ends of the mandrel and clos ure may be connected to separate valves, and sight glasses may be located between each valve and its corresponding en With the first closure in place, the annular space surrounding the mandrel is filled with proper sized oxidizer. The other closure then is put into place and one valve is closed while the other is connected to a vacuum so as to withdraw all air from the mass of oxidizer. The end of the apparatus containing the closed valve is then connected to a source of a polymerizable or solidifiable liquid fuel-binder. By way of example, some of the best known binders are asphalt, phenolic resin, polystyrene, synthetic rubbers, urea-aldehydes, vinyl polymers and nitrocellulose. The term polymerizable is intended to encompass a fuel-binder which will flow into the container and then can be solidified therein.

The vacuum acts to draw in the liquid fuel-binder until it appears in the sight glass adjacent the valve directly connected to the vacuum source when both valves are closed. The entire device is then raised to the proper temperature where it is maintained for the proper time to polymerize or to efiect solidification of the fuel-binder.

As mentioned, the mandrel and closures may be made of a low melting point alloy such as Roses or Woods metal, or they may be made in the form of a solid core coated with a special paint which paint will release the core when raised to a predetermined temperature. After polymerization or solidification of the fuelbinder, the entire apparatus may be heated above the melting point of the material of the mandrel and closure, whereupon the mandrel and closure are melted and collected for reuse, leaving the motor filled with a highly efficient solid propellant.

The above, other objects and novel features of the invention will become apparent from the following specification and accompanying drawing which is merely exemplary.

In the drawing:

FIG. 1 is a longitudinal sectional view of a rocket motor at one stage of the method of this invention;

FIG. 2 is a view similar to FIG. 1 at another stage of the method of this invention;

FIG. 3 is a diagrammatic view of certain steps in the process; and

FIG. 4 is a longitudinal sectional view of the completed rocket motor embodying the principles of the invention.

Referring to FIG. 1, the principles of the invention have been shown as applied to a rocket motor comprising a casing 10 which is shown as being tubular in form. The casing 10 may be made from any suitable material such as stainless steel, titanium, certain low alloy steels containing vanadium in conjunction with chromium, nickel and molybdenum as well as other materials.

The casing 10 may include internal threads 11 and 12 at each end thereof. A closure mandrel 13 having a stem 14 may be threaded into one end of the casing 10 with its stem 14 extending along the longitudinal centerline of the casing 10, forming an annular space 15 between stem 14 and the inner wall of the casing.

The mandrel 13 may include a passage 16 that includes two or more branches 17, 18 leading to the annular space 15. A tubular sight glass 19 may have its one end held in abutting relation with the one end of mandrel 13 with its tubular passage aligned with the passage 16 by a plastic, rubber or other flexible tubular element 20. The other end of the sight glass 19 may be connected in a similar fashion to a valve 21 for a purpose to be described later.

The annular chamber or space 15 may be filled with a granular oxidizer. As previously mentioned, the commonly used oxidizers for solid propellant fuel are potassium perchlorate, ammonium perchlorate and ammonium nitrate, although sodium and potassium nitrates have been used. When additives are to be employed which are not soluble, emulsionable or suspendable in the liquid fuelbinder, they may be, of course, mixed with the granular oxidizer.

Referring to FIG. 2, a closure 22 may be threaded into the end of casing containing the threads 12. It may completely fill the casing 10 above the level of the oxidizer Within the annular space 15. The closure 22 may include a passage 23 with branches 24, 25 leading to space 15. The outer end of closure 22 may have another sight glass 26 connected to it and a valve 27 in the same way that sight glass 19 is connected to valve 21.

With the apparatus in the condition shown in FIG. 2, valve 21 is closed and valve 27 is open and connected to a vacuum pump (not shown). This will effect the evacuation of the air and gas within space between the granules of powdered oxidizer. After .a sufficient time to evacuate the space 15, the valve 21 is connected to a source of polymerizable liquid fuel-binder and opened.

The fuel-binder forms a matrix of plastic, resinous or elastomeric material. The matrix provides fuel for the combustion reaction. Both thermosetting and thermoplastic substances may be used. Such binder materials may be classified as (1) asphalt oil types, (2) cellulosic derivatives, (3) synthetic resins, (4) elastomers, and (5) polyesters. When additives are to be used which are soluble, emulsionable or suspendable in the fuel-binder, they may be incorporated therein. The polymerizable liquid fuel-binder is drawn upwardly through passages 16, 17 and 18 by the vacuum acting through valve 27, thereby filling all of the interstices between the granules of oxidizer, providing a thoroughly and evenly dispersed fuelbinder throughout the mass of oxidizer within the space 15. The liquid fuel-binder then passes upwardly through the passages 24, 25, 23 in the closure 22, and when it is observed in sight glass 26, valve 21 and 27 are closed and the assembly is disconnected from the vacuum pump and the source of liquid fuel-binder.

The mandrel 13, stem 14 and closure 22 are made from a low melting point alloy material but having a melting point substantially above the polymerization temperature of the liquid fuel-binder, such as Roses or Woods metal, or it may be a solid core coated with a special paint which will release the core when heated to a predetermined temperature.

The casing 10, mandrel 13 and closure 22 may then be placed within a furnace 28 shown diagrammatically in FIG. 3, and raised to a temperature and held there for a sufiicient length of time to effect polymerization of the liquid fuel-binder, thus causing it to adhere to the internal surface of the casing 10. After complete polymerization of the fuel-binder, the temperature within furnace 28 may be raised to the melting point of the material from which mandrel 13, stem 14 and closure 22 are made. This molten material may be collected for reuse, and the gates formed by the passages 16, 17, 18 and 23, 24, 25 are removed from the ends of the charge within the annular space 15, forming the completed rocket motor as shown in FIG. 4.

Alternatively, the mandrel 13, stem 14 and closure 22 may also be made from a solid core having a special coat of paint that will, when the device is raised above the polymerization temperature of the fuel-binder, permit the ready removal of the closures 13 and 22 in their solid form. Again, these elements 13, 14 and 22 may be made of a material that will dissolve in a solvent that will not react with the propellant grains and therefore can be removed by immersing the filled casing within such a solvent.

By way of example, the oxides employed may be 75 parts by volume of potassium perchlorate, 24 parts by volume of vinyl polyester, and the remainder sodium luaryl sulphate and powdered aluminum.

Although the various features of the new and improved method for making rocket motors for missiles have been shown and described in detail to fully disclose several emlemma 1 4. bodiments of the invention, it will be evident that changes may be made in such details and certain features may be used without others without departing from the principles of the invention.

What is claimed is:

1. The method of making solid propellant fuel filled rocket motors which comprises filling a casing with granular oxidizer; applying closure members having passage means therethrough to each end of said casing made from a material capable of being changed into a different phase facilitating removal; applying a vacuum through one of said closures to evacuate all air and gas between said granules; while said vacuum is being applied through said one closure, admitting an unreacted polymerizable liquid fuel-binder through the other closure until the interstices between said granules are completely filled; heating said unreacted liquid filled casing to a sufi'icient temperature and for a sufiicient time to effect polymerization of said fuel-binder; and thereafter subjecting said assembly to a condition effecting a phase change of said closure members for removing the same.

2. The method of making solid propellant fuel filled rocket motors which comprises filling a casing with granular oxidizer; applying closure members having passage means therethrough to each end of said casing made from a material having a relatively low melting point; applying a vacuum through one of said closures to evacuate all air and gas between said granules; while said vacuum is being applied through said one closure, admitting an unreacted polymerizable liquid fuel-binder through the other closure until the interstices between said granules are completely filled; the polymerization temperature of said liquid being lower than said melting point; heating said unreacted liquid filled casing to a sufficient temperature and for a sufiicient time to effect polymerization of'said fuel-binder; and thereafter raising the temperature of said filled casing to said melting point where said closures melt and drain from said casing.

3. The method of making solid propellant fuel filled rocket motors which comprises filling a casing with granular oxidizer; applying closure members having passage means therethrough to each end of said casing made from a material that is soluble in a solvent that does References Cited by the Examiner UNITED STATES PATENTS 830,432 9/ 1906 Hennessey. 1,475,764 11/ 1923 Frederick. 1,554,697 9/1925 Alden. f 2,916,776 12/ 1959 ONeill et al. 3,021,748 2/ 1962 Miller. 3,027,597 4/1962 McCurdy.

CARL D. QUARFORTH, Primary Examiner. ALEXANDER H. BRODMERKEL, wry 1AM J. STEPHE SO AURICE A.- RI DISI, m e 

1. THE METHOD OF MAKING SOLID PROPELLANT FUEL FILLED ROCKET MOTORS WHICH COMPRISES FILLING A CASING WITH GRANULAR OXIDIZER; APPLYING CLOSURE MEMBERS HAVING PASSAGE MEANS THERETHROUGH TO EACH END OF SAID CASING MADE FROM A MATERIAL CAPABLE OF BEING CHANGED INTO A DIFFERENT PHASE FACILITATING REMOVAL; APPLYING A VACUUM THROUGH ONE OF SAID CLOSURES TO EVACUATE ALL AIR AND GAS BETWEEN SAID GRANULES; WHILE SAID VACUUM IS BEING APPLIED THROUGH SAID ONE CLOSURE, ADMITTING AN UNREACTED POLYMERIZABLE LIQUID FUEL-BINDER THROUGH THE OTHER CLOSURE UNTIL THE INTERSTICES BETWEEN SAID GRANULES ARE COMPLETELY FILLED; HEATING SAID UNREACTED LIQUID FILLED CASING TO A SUFFICIENT TEMPERATURE AND FOR A SUFFICIENT TIME TO EFFECT POLYMERIZATIN OF SAID FUEL-BINDER; AND THEREAFTER SUBJECTING SAID ASSEMBLY TO A CONDITION EFFECTING A PHASE CHANGE OF SAID CLOSURE MEMBERS FOR REMOVING THE SAME. 